IP based PBX has gained acceptance and momentum in the market place of advanced, high speed communications. The architecture of an prior art IP-PBX system is seen in FIG. 1. The system 100 consists of a number of IP phones (101, 102, 103) which are connected to a local area network (LAN) 120. Connected to the LAN is a server 110 which provides control of the local telephony network. The server 110 communicates with IP phones (101, 102, 103) via IP messages, accepts call requests from the IP phones (101, 102, 103) and alerts the phones upon incoming calls. There are two common standards for this protocol: H.248 from the International Telephone Union (ITU) and Session Invitation Protocol (SIP) from the Internet Engineering Task Force (IETF). The intelligence of the system 100 resides in the server 110 which can provide enhanced services such as call waiting, call hold, call transfer and the like.
In IP-PBX, voice traffic is encapsulated inside IP packets and is carried between the IP phones using the LAN. For communications to phones in the public switched telephone network (PSTN), a gateway 130 is needed to convert the IP encapsulated voice traffic to the traditional time division multiplexed (TDM) format. The gateway 130 is also under control of the server 110 using H.248. The usual access protocol between the gateway 130 and the PSTN is ISDN PRI. Many traditional PBXs have been upgraded to have an IP interface to support IP phones. These PBXs are considered as IP-PBX in this convention.
As IP-PBXs are created, the need to connect all the PBXs within an enterprise together to form a corporate network exists (just as it did with respect to TDM based systems). An advantage in connecting two IP-based PBXs is that the voice traffic is already packetized. Direct packet-to-packet connectivity is desirable as there is no need to convert the voice packets to TDM and back to again. A packet to TDM gateway is not necessary for calls between the IP-PBXs. This results in cost reduction and improvement in the performance of the system, as this avoids costly packet to TDM conversion and vice versa.
In one of the approaches to interconnect IP-PBXs, the user subscribes to connection oriented packet services, such as frame relay and ATM permanent virtual circuit services, from a service provider (SP). The SP would only provide transport services for the packet and is not aware that the packets are voice packets. In an alternate approach in which the SP can provide added functionality, the SP would actively participate in the call signaling when a call is being in set up. In doing so, the SP can provide enhanced service at the request of the end-user on a call-by-call basis. As the SP network is aware of when calls are set up and torn-down, the service can be charged based on call duration. This may result in lower cost to the end-user, another benefit. In the TDM environment, this alternative is similar to the “Software Defined Network” services from the SPs where TDM based PBXs are connected to the SP's networking using the Primary Rate Interface (PRI) from the ISDN. We will refer to this alternative as VoIP-VPN.
The module in this network that handles call signaling from the user is commonly referred to as a soft-switch. Depending on the size of the network, a network may contain a number of soft-switches, which are interconnected. Call signaling messages route through a series of soft-switches in order to establish a call as it is more efficient to connect the IP PBXs through an IP network, without converting the voice traffic to TDM and back.
In the current state of the art, all the IP phones are assigned an IP address from the SP's IP address space. However, this is a major shortcoming. Most enterprises use their own IP addressing scheme in addressing their workstations and PCs. All IP-VPN services allow the customer to use their own IP address scheme. Customer would like any VoIP-VPN service to have the same capability, i.e, the IP phones can be assigned IP address from the customer IP address space instead of the SP's public IP address space. This capability is important as, in the future, that an IP phone would actually be part of a PC or workstation. In this case, it is paramount that the PC and the IP phone use the same IP address or, at least, use IP address from the same addressing space. This invention describes an innovative method to do this.